An organic thin-film transistor circuit for large-area temperature-sensing

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (leaves 81-84).This thesis explores the application of organic thin-film transistors (OTFTs) for temperature-sensing. The goal of this work is twofold: the understanding of the OTFT's electrical characteristics' temperature dependence, and the creation of OTFT temperature-sensing circuits. We find that OTFTs have temperature-dependent current-voltage (I-V) characteristics that are determined by trap states inside the bandgap. Based on this understanding, a DC OTFT circuit model is developed which accurately fits the measured I-V data in all regions of device operation and at different temperatures. Using this model, we design and fabricate two OTFT temperature-sensing circuits. The first circuit achieves a responsivity of 22mV/°C with 12nW of power dissipation, but has a nonlinear temperature response that is dependent on threshold voltage shifts. The second circuit achieves a responsivity of 5.9mV/°C with 88nW of power dissipation, and has a highly linear temperature response that is tolerant of threshold voltage shifts. Both circuits exceed silicon temperature sensors' typical temperature responsivity of 0.5 - 4mrV/C while dissipating less power. These traits, along with the OTFT's ability to be fabricated on large-area and flexible substrates, allow OTFT temperature sensors to be used in both existing and new application environments.by David Da He.S.M